Abstract
Enterotoxigenic Escherichia coli (ETEC) is the most common and global cause of neonatal calf diarrhea, but there is little information regarding calf ETEC strains in Argentina. In this study, five ETEC isolates from diarrheic dairy calves (2-10 days-old) from Buenos Aires and Cordoba, Argentina, were characterized on the basis of virulence gene (VG) pattern, O:H serotyping, hemolytic phenotype, phylogenetic group affiliation, antimicrobial resistance profile and presence of integron class 1 and 2.
The five isolates were examined by PCR for the presence of 18 bovine VGs and showed the following genotypes: F5+/F41+/sta+ (D242), F5+/sta+ (D158), F5+/sta+ (D157), F5+ (D151-9) and F5+/iucD+ (D151-5). These VGs confer pathogenic potential and most of them are associated with the ETEC pathotype. The five isolates showed a non-hemolytic phenotype, belonged to five different serotypes: O101:H-, O141:H-, O60:H-, ONT:H10, ONT:H- and were assigned to the phylogenetic group A by the quadruplex Clermont PCR method. The antimicrobial (AM) resistance of the three isolates D242, D157 and D151-5 was determined by agar disk diffusion method for 24 AMs and they exhibited a multiresistance phenotype (resistance to 4 different AM classes: Cephalosporins, Penicillins, Macrolides and Ansamycins). In addition, class 1 integrons were found in the isolate D151-5 containing the dfrA17-aadA5 gene cassette and in the bovine ETEC reference strain FV10191 containing the dfrA1-aadA1 gene cassette. The present study revealed for the first time the occurrence of multiresistant ETEC associated with neonatal diarrhea in dairy calves in Argentina. This finding may be used for diagnostic and therapeutic purposes.

Key words: Escherichia coli, dairy cattle, neonatal diarrhea, virulence gene, antimicrobial resistance.